Hi,
I'm new to Maven and I'm currently going through the "Getting Started"
guide.
While reading, the following question came to me.
As far as I understand, Maven defaults to compiling all Java source
files with compatibility for JDK 1.3 (i.e., -source 1.3).
The guide explains how to change that behaviour, by configuring the
maven-compiler-plugin in the pom.xml:
http://maven.apache.org/guides/getting-started/index.html#How_do_I_use_plug-ins
So far so good. However, if I do this, it appears that I also have to
specify the version of maven-compiler-plugin to be used (e.g., 2.5.1 in
the code snippet shown under the above link).
Generally, I don't want to do that. On the one hand, I would like for
Maven to simply use the latest version of the maven-compiler-plugin that
is available (the default behaviour). On the other hand, I would like to
use Java features above 1.3 (for instance, generics).
So my first attempt was to simply remove the "<version>2.5.1</version>"
part from the pom.xml under the maven-compiler-plugin configuration.
While this did in principle work, Maven was not happy at all and
complained with this message:
[WARNING] Some problems were encountered while building the effective
model for com.mycompany.app:my-app:jar:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for
org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 19,
column 15
[WARNING]
[WARNING] It is highly recommended to fix these problems because they
threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support
building such malformed projects.
So my question boils down to this: is there some way for me to achieve
the following three things at the same time:
(1) have Maven compile my source files with -source 1.4 (or anything
higher than 1.3)
(2) *not* specify the maven-compiler-plugin version to use; instead,
have Maven dynamically use the latest one available;
(3) *not* have Maven bitch about my project being "malformed" ;-)
I would imagine that this is not such a rare scenario:
(1) I do want to use Java features higher than those available in Java 1.3;
(2) I do *not* want having to monitor the maven-compiler-plugin by
myself all the time in order to check for updates and keep my pom.xml
referring to the currently latest version;
(3) yet I do *not* want Maven complaining about my project.xml being
malformed either.
So what's the "clean" way to do this? :-)
For clarity, I have written down the steps to reproduce my problem in
the Appendix, below.
Thanks,
Malte
APPENDIX: Steps to reproduce:
1. Generate a simple Maven project using the very command stated on
http://maven.apache.org/guides/getting-started/index.html#How_do_I_make_my_first_Maven_project
:
mvn archetype:generate \
-DarchetypeGroupId=org.apache.maven.archetypes \
-DgroupId=com.mycompany.app \
-DartifactId=my-app
2. Replace the generated src/main/java/com/mycompany/app/App.java with
something that uses generics (not available in Java 1.3), e.g.:
package com.mycompany.app;
import java.util.*;
/**
* Hello world!
*
*/
public class App {
public static void main( String[] args) {
List<String> myList = new ArrayList<String>();
myList.add( "Hello");
myList.add( "world");
for( Iterator<String> i = myList.iterator(); i.hasNext();)
System.out.println( i.next());
}
}
3. Try to compile using the command 'mvn compile'. Maven fails:
$ mvn compile
[INFO] Scanning for projects...
...
[INFO]
------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO]
------------------------------------------------------------------------
[INFO] Total time: 0.995s
[INFO] Finished at: Tue Nov 26 15:26:00 CET 2013
[INFO] Final Memory: 6M/117M
[INFO]
------------------------------------------------------------------------
[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile
(default-compile) on project my-app: Compilation failure
[ERROR]
/home/malte/dev/java/testMaven/my-app/src/main/java/com/mycompany/app/App.java:[13,5]
error: generics are not supported in -source 1.3
...
4. Ok, so let's add the following to our pom.xml. This is copied&pasted
from
http://maven.apache.org/guides/getting-started/index.html#How_do_I_use_plug-ins
:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.5.1</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
Running 'mvn compile' again, everything works fine now.
5. Yet, I would like to avoid having to specify the version of
maven-compiler-plugin to be used. I simply want Maven to use the latest
one available. So, let's remove the line
<version>2.5.1</version>
from the pom.xml again.
Running 'mvn compile' again, this works too, but Maven complains:
$ mvn compile
[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective
model for com.mycompany.app:my-app:jar:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for
org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 19,
column 15
[WARNING]
[WARNING] It is highly recommended to fix these problems because they
threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support
building such malformed projects.
[WARNING]
...
[INFO]
------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO]
------------------------------------------------------------------------
[INFO] Total time: 0.877s
[INFO] Finished at: Tue Nov 26 15:37:17 CET 2013
[INFO] Final Memory: 5M/117M
[INFO]
------------------------------------------------------------------------
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